School of Energy Science and Engineering, Henan Polytechnic University, Jiaozuo, China.
Collaborative Innovation Center of Coal Work Safety, Jiaozuo, China.
PLoS One. 2024 Sep 19;19(9):e0310694. doi: 10.1371/journal.pone.0310694. eCollection 2024.
In order to study the shear mechanical properties of rock joint under different unloading stress paths, the RDS-200 rock joint shear test system was used to carry out direct shear tests on concrete joint specimens with five different morphologies under the CNL path and different unloading stress paths. The unloading stress paths include unloading normal load and maintaining constant shear load (UNLCSL), unloading normal load and unloading shear load (UNLUSL), unloading normal load and increasing shear load (UNLISL). The results show that the peak shear strength, cohesion, internal friction angle, pre-peak shear stiffness and residual shear strength of concrete joints under CNL path increases with the increasing JRC and normal stress. Under the UNLCSL path, under the same initial shear stress τ1, instability normal stress σi decreases with the increasing JRC, and normal stress unloading amount Δσn increases with the increasing JRC. Under the same JRC, σi increases with the increase of τ1, and Δσn decreases with the increasing τ1. Under the same JRC and σi, τi is significantly smaller under the UNLCSL path than the CNL path. Under the same JRC, the cohesion under the UNLCSL path is less than the CNL path, and the internal friction angle is higher than that the CNL path. Under the same JRC and σi, τi is the largest under the path of CNL and UNLISL, followed by the UNLCSL path, and τi under the UNLUSL path is the smallest. Compared with the CNL path, the variation range of the specimen internal friction angle is within 3% while the average decrease percentage of the specimen cohesion reaches 37.6% under the UNLCSL path, UNLISL, and UNLUSL. Therefore, it can be inferred that the decrease in cohesion caused by normal unloading is the main reason for the decrease in joint instability shear strength. After introducing the correction coefficient k of cohesion to modify the Mohr-Coulomb criterion, the maximum average relative error after correction is only 3.5%, which is significantly improved compared with the maximum average relative error of 56.9% before correction. The research conclusions can provide some reference for the accurate estimation of shear bearing capacity of rock joints under different unloading stress paths, which is of great significance to the stability evaluation and disaster prevention of rock mass engineering.
为了研究不同卸荷应力路径下岩石节理的剪切力学特性，利用 RDS-200 岩石节理直剪试验系统，对 5 种不同形貌的混凝土节理试件在 CNL 路径和不同卸荷应力路径下进行了直剪试验。卸荷应力路径包括卸荷法向载荷并保持恒定剪切载荷（UNLCSL）、卸荷法向载荷并卸荷剪切载荷（UNLUSL）和卸荷法向载荷并增加剪切载荷（UNLISL）。研究结果表明，在 CNL 路径下，随着节理粗糙度 JRC 和法向应力的增加，混凝土节理的峰值剪切强度、黏聚力、内摩擦角、预峰剪切刚度和残余剪切强度均增大。在 UNLCSL 路径下，在相同的初始剪切应力τ1 下，失稳法向应力σi 随 JRC 的增加而减小，法向卸荷量Δσn 随 JRC 的增加而增大。在相同的 JRC 下，σi 随τ1 的增加而增大，Δσn 随τ1 的增加而减小。在相同的 JRC 和σi 下，UNLCSL 路径下的τi 明显小于 CNL 路径下的τi。在相同的 JRC 下，UNLCSL 路径下的黏聚力小于 CNL 路径下的黏聚力，内摩擦角大于 CNL 路径下的内摩擦角。在相同的 JRC 和σi 下，CNL 和 UNLISL 路径下的τi 最大，UNLCSL 路径次之，UNLUSL 路径下的τi 最小。与 CNL 路径相比，UNLCSL、UNLISL 和 UNLUSL 路径下试件内摩擦角的变化范围均在 3%以内，而试件黏聚力的平均降幅则达到 37.6%。因此，可以推断出法向卸荷引起的黏聚力降低是导致节理失稳剪切强度降低的主要原因。引入黏聚力修正系数 k 修正 Mohr-Coulomb 准则后，修正后的最大平均相对误差仅为 3.5%，与修正前的最大平均相对误差 56.9%相比有了显著提高。研究结论可为不同卸荷应力路径下岩石节理剪切承载能力的准确估算提供一定的参考，对岩体工程的稳定性评价和灾害防治具有重要意义。
